DNS structure guide
Subdomain vs domain: what changes technically and for search?
Reviewed 10 September 2026 · 6-minute read
A registered domain is obtained through a registrar; a subdomain is a DNS name beneath a domain you already control. In app.example.com, example.com is the registrable domain in the common `.com` case and app is a subordinate label. A URL can contain either hostname plus a path, query and fragment.
Side-by-side
| Question | Registered domain | Subdomain |
|---|---|---|
| Example | example.com | docs.example.com |
| Created through | Registry/registrar transaction | DNS or hosting configuration under existing control |
| Separate registration fee | Usually yes, with renewal | Not normally; provider usage fees can still apply |
| Can point elsewhere | Yes | Yes, through its own DNS records or delegation |
| Search structure | Domain-level site | Can be operated and measured as a distinct site |
Subdomain vs subdirectory
docs.example.com is a different hostname; example.com/docs/ is a path on the same hostname. A subdomain can simplify separate deployments, teams or security boundaries. A subdirectory can simplify shared navigation, cookies, analytics and content ownership. Neither structure fixes weak content or poor crawlability.
What Google says
Google's crawling and indexing FAQ says it has no preference between subfolders and subdomains for crawling, indexing and ranking, provided they can be crawled. Choose based on how the site is easiest to organize and manage. In practice, whichever option you choose still needs coherent internal links, canonicals, sitemaps and ownership.
Operational differences to plan
- TLS: each hostname must be covered by an appropriate certificate.
- DNS: a subdomain can use direct records, aliases or a delegated zone.
- Cookies: host-only cookies stay on one hostname; broader Domain attributes can cross subdomains and should be used deliberately.
- Security: separate applications can still affect one another through shared cookies, CORS, content-security policy and domain trust.
- Measurement: analytics and Search Console configuration should match the selected ownership boundary.
Do not use registration lookup for a subdomain
RDAP and WHOIS are registration-data systems. A subordinate hostname can exist without its own registry object, and a missing object does not make the label independently purchasable. Use SeekDom for the registrable name you plan to buy; use DNS tools to investigate hostnames beneath it.
Frequently asked questions
Do I need to register each subdomain?
No. Control of a registered domain normally lets its DNS operator create subordinate names, subject to DNS, hosting, certificate and provider limits. A subdomain is not bought as a separate registry registration.
Does Google prefer subdirectories or subdomains?
Google says it has no preference for crawling, indexing and ranking. Choose the structure that is easiest to organize and operate, while accounting for ownership, deployment, cookies, analytics and security boundaries.
Can SeekDom check a subdomain?
SeekDom queries registration services, not DNS hosting. Enter the registrable domain you might buy. An RDAP no-match for a hostname such as app.example.com does not mean that subdomain can be purchased.